With the demand for weight saving, miniaturization and high-density packaging of electronic apparatus in recent years, replacement of inorganic glass with optically transparent resins is proceeded in fields of optical parts and liquid crystal display parts such as lenses, backlights, light guide plates and liquid crystal substrates, in which the inorganic glass has heretofore been used. Use of transparent resins in the form of sheets, films, thin films or the like is also increasing.
As transparent resins for optical materials, polyacrylates, polycarbonate and the like have heretofore been widely used. However, the transparent resins for replacement of the inorganic glass are required to improve properties such as heat resistance, resistance to moisture absorption, adhesive property and breaking strength in addition to transparency.
In order to meet such requirements, it is begun to use cycloolefin polymers as optical materials.
For example, addition polymers of cycloolefin compounds such as bicyclo[2.2.1]hept-2-ene (norbornene) are proposed as cycloolefin polymers excellent in transparency and heat resistance (see, for example, the following Prior Art. 1, Prior Art. 2, Prior Art. 3 and Prior Art. 4).
However, these cycloolefin addition polymers exhibit a glass transition temperature exceeding 300° C., and so they have very high heat resistance, but involve such problems that thermal molding and forming such as injection molding and extrusion molding become difficult on the other hand.
As polymers of a cycloolefin compound, are known addition copolymers of the cycloolefin compound and an acyclic olefin compound such ethylene (see, for example, the following Prior Art. 5, Prior Art. 6 and Prior Art. 7). As polymerization catalysts for obtaining these cycloolefin addition copolymers, are known catalyst systems containing zirconium, titanium or vanadium, such as metallocene.
Since these catalyst systems scarcely exhibit polymerizing ability to monomers containing polar groups such as an ester group and alkoxysilyl groups, however, it is difficult to impart functions such as adhesive property to the resulting copolymer or introduce crosslinking groups such as a hydrolyzable silyl group. In addition, the cycloolefin addition copolymers may become low in transparency due to crystallinity of an ethylene chain, or the like in some cases and are not always suitable for use as optical materials.
As cycloolefin polymers useful as optical materials for producing lenses, optical disks and the like, ring-opened (co)polymers of a cycloolefin compound or hydrogenated products thereof are proposed (see, for example, the following Prior Art. 8, Prior Art. 9, Prior Art. 10, Prior Art. 11, Prior Art. 12 and Prior Art. 13). These ring-opened cycloolefin (co)polymers or hydrogenated products thereof are excellent in heat resistance, low in water (moisture) absorption property, also excellent in optical properties such as transparency and further excellent in property as to molding such as injection molding. However, such ring-opened cycloolefin (co)polymers or hydrogenated products thereof are low in affinity for other materials because they have no polar group, and involve a problem in properties as to post processing such as adhesion, printing and vapor deposition.
In order to solve such a problem, those with a polar group introduced in their molecules are proposed as ring-opened cycloolefin (co)polymers or hydrogenated products thereof (see, for example, the following Prior Art. 14 and Prior Art. 15). Since these ring-opened cycloolefin (co)polymers or hydrogenated product thereof are excellent in heat resistance and optical properties and also in property as to molding such as injection molding, and moreover excellent in affinity for other materials compared with the ring-opened cycloolefin (co)polymers or hydrogenated products thereof having no polar group, they are also excellent in properties as to post processing such as adhesion. However, such ring-opened cycloolefin (co)polymers or hydrogenated products thereof are low in mechanical strength, so that a problem may arise in some cases when thin molded products such as sheets or films are formed.
On the other hand, dicyclopentadiene (alias: tricyclo[5.2.1.02.6]deca-3,8-diene) is a compound widely used as a starting material in synthesis of a monomer for obtaining the above-described cycloolefin polymers.
When dicyclopentadiene (hereinafter also referred to as “DCP”) itself is used as a monomer for obtaining a cycloolefin polymer, however, a gelled product or a polymer having branches may be formed in some cases because DCP has 2 olefinic double bonds in its molecule. Therefore, when DCP is used as a raw material for industrially producing a cycloolefin polymer, there is a problem that it may interfere with the production of the cycloolefin polymer.
In order to solve the problem caused by the presence of a plurality of olefinic double bonds, ring-opened (co)polymers and hydrogenated products thereof obtained by ring-opening (co)polymerization of tricyclo[5.2.1.02.6]dec-3-ene, in which a double bond of a norbornene ring in DCP is hydrogenated, and only a double bond in the 5-membered ring remains are proposed (see, for example, the following Prior Art. 16).
However, such a ring-opened (co)polymer is that obtained through ring-opening the 5-membered ring in tricyclo[5.2.1.02.6]dec-3-ene, and its hydrogenated product contains a chain of 3 methylene groups in the structural unit, so that a problem that only a polymer relatively low in glass transition temperature can be obtained arises.
In DCP, 2 stereoisomers of an exo form and an endo form exist. In both hydrogenated products of their ring-opened polymers, the glass transition temperatures are 97° C. and 66° C., respectively, and are lower than 100° C. It is thus difficult to use them as materials of which heat resistance is required (see, for example, the following Prior Art. 17). Further, polymers that are hydrogenated products of ring-opened (co)polymers, in which a proportion of a structural unit derived from DCP is at least 70% by weight, and a proportion of the endo form in the DCP used is at least 50% by weight, are proposed. According to such hydrogenated products of the ring-opened (co)polymers, it is said that an effect of improving mechanical strength such as impact strength is brought about (see, for example, the following Prior Art. 18). However, the glass transition temperatures of these ring-opened (co)polymers are all lower than 120° C., and so they do not have any performance satisfied as materials of which heat resistance is required.
Prior Art. 1: Japanese Patent Application Laid-Open No. 63807/1992;
Prior Art. 2: Japanese Patent Application Laid-Open No. 198919/1996;
Prior Art. 3: Japanese Patent Application Laid-Open No. 508649/1997 (through PCT route);
Prior Art. 4: Japanese Patent Application Laid-Open No. 505880/1999 (through PCT route);
Prior Art. 5: Japanese Patent Application Laid-Open No. 292601/1986;
Prior Art. 6: U.S. Pat. No. 2,883,372;
Prior Art. 7: Makromol. Chem. Macromol. Symp., Vol. 47, p. 83 (1991);
Prior Art. 8: Japanese Patent Application Laid-Open No. 21878/1988;
Prior Art. 9: Japanese Patent Application Laid-Open No. 138257/1989;
Prior Art. 10: Japanese Patent Application Laid-Open No. 168725/1989;
Prior Art. 11: Japanese Patent Application Laid-Open No. 102221/1990;
Prior Art. 12: Japanese Patent Application Laid-Open No. 133413/1990;
Prior Art. 13: Japanese Patent Application Laid-Open No. 170425/1992;
Prior Art. 14: Japanese Patent Application Laid-Open No. 111200/1975;
Prior Art. 15: Japanese Patent Application Laid-Open No. 132626/1989;
Prior Art. 16: Japanese Patent Application Laid-Open No. 196779/1995;
Prior Art. 17: Polymer J., Vol. 27, No. 12, p. 1167 (1995);
Prior Art. 18: Japanese Patent Application Laid-Open No. 130846/1999.